Helmholtz Resonator-Based Triboelectric Nanogenerator For Highly Efficient Harvesting Of Acoustic Energy

Sound waves are ubiquitously present in our surroundings.Unfortunately,most sound wave energy has been wasted because of its very low energy density and the lack of effective technologies for harvesting acoustic energy.If this widely distributed and pollution-free energy is utilized,and converted into electric energy.It will provide important ideas for self-powering the Io T nodes or extending battery life.A dual-tube Helmholtz resonator-based triboelectric nanogenerator（HR-TENG）for highly efficient harvesting of acoustic energy is designed in this thesis.This HR-TENG is composed of a Helmholtz resonant cavity,a metal film with evenly distributed acoustic holes and a dielectric soft film with one side ink-printed for electrode.The FEP（Fluorinated ethylene propylene）film in the Helmholtz cavity alternatively contacts and separates from the aluminum film under the excitation of an acoustic wave.The built-in electric field between the two films continuously changes,driving electrons to flow in the external circuit,thus generating an electrical output.Effects of resonant cavity structure,acoustic conditions,and film tension on the HR-TENG performance are investigated systematically.By coupling the mechanisms of triboelectric nanogenerator and acoustic propagation,a theoretical guideline is provided for improving energy output and broadening the frequency band.In terms of cavity structure,compared to the TENG based on the conventional Helmholtz resonator,the dual-tube HR-TENG has a much better output performance,with the maximum output voltage increasing by 83%.In acoustic conditions,the output dependence on the acoustic frequency and sound pressure has been clarified.When the acoustic wave frequency is fixed,larger displacement and deformation of the FEP film are expected with an increase in the sound pressure,and thus,a higher output performance is achieved.However,for a fixed acoustic wave amplitude,the effect of the acoustic frequency on the electrical output of the HR-TENG is not unidirectional.Thus,a peak output voltage exists with increasing acoustic frequency.Under the optimal output frequency of 70 Hz and sound pressure level of 85.3 d B,the open-circuit voltage and short-circuit current can reach 132 V and 32μA,respectively.The tension force also has a marked impact on the output performance of the HR-TENG.The optimal frequency shift rule has the same trend as the characteristic frequency of the film.After increasing the tension force of the FEP film,the optimal output frequency is shifted to a larger value.Furthermore,by reducing the geometric size of the resonator,the response frequency of the HR-TENG can reach more than 500 Hz.The output performances of a micro-electromagnetic generator,piezoelectric nanogenerators and TENGs for acoustic energy harvesting are compared.The TENGs show very good output performances and application potential in the acoustic energy harvesting area.With the optimized design,the HR-TENG can generate a maximum acoustic sensitivity per unit area of 1.23 VPa^-1cm^-2 and a power density per unit sound pressure of 1.82 WPa^-1cm^-2,which are higher than the best results from the literature by 60%and 20%,respectively.Furthermore,the HR-TENG has been proven to serve as a self-powered active sensor for acoustic recording and diesel engine operation monitoring.Therefore,this thesis not only provides effective guidelines for converting acoustic energy into electricity with high efficiency but also presents potential applications of the HR-TENG in acoustic sensing.